Photoflash lamp and method of preparing and applying fulminating material

ABSTRACT

A percussive-type photoflash lamp, the primer of which comprises a wire anvil partially coated with fulminating material and coaxially supported within a tube in a manner providing a clearance between the coating of fulminating material and the inner wall of the tube. The fulminating material includes a red phosphorus fuel, a chlorate salt oxidizer, a powder combustible, incandescible metal, and a powdered carbon additive for facilitating propulsion of the powdered metal from the primer tube into the lamp envelope when ignited. The fulminating material is prepared and applied in the following manner: the red phosphorus, powdered metal and powdered carbon area dispersed in water to provide an aqueous slurry; the anvil wire is dipped into this aqueous slurry; the coating is dried; a dissolved chlorate salt solution is prepared; and the coated wire is dipped into the chlorate solution so as to permeate the previously applied coating.

United States Patent Shaffer 5] Feb. 29, 1972 Primary Examiner-Edward.1. Michael Attorney-Norman J. O'Malley and Edward J. Coleman [57]ABSTRACT A percussive-type photollash lamp, the primer of whichcomprises a wire anvil partially coated with fulminating material andcoaxially supported within a tube in a manner providing a clearancebetween the coating of fulminating material and the inner wall of thetube. The fulminating material includes a red phosphorus fuel, achlorate salt oxidizer, a powder combustible, incandescible metal, and apowdered carbon additive for facilitating propulsion of the powderedmetal from the primer tube into the lamp envelope when ignited. Thefulminating material is prepared and applied in the following manner:the red phosphorus, powdered metal and powdered carbon area dispersed inwater to provide an aqueous slurry; the anvil wire is dipped into thisaqueous slurry; the coating is dried; a dissolved chlorate salt solutionis prepared; and the coated wire is dipped into the chlorate solution soas to permeate the previously applied coating.

12 Claims, 1 Drawing Figure PAIENTEDFEBZS I972 I 3, 645,663

JOHN W SHAFFER VENTOR AGENT PHO'IOFLASII LAMP AND METHOD OF PREPARINGAND APPLYING FULMINATING MATERIAL This invention relates to themanufacture of percussive-type photoflash lamps and more particularly tothe composition of the fulminating material employed therewith,especially as associated with the method of preparing and applying thefulminating material.

Generally speaking, a percussive-type photoflash lamp comprises anhermetically sealed, light transmitting envelope containing a source ofactinic light and having a primer secured thereto. More particularly,the percussive-type photoflash lamp comprises a length of glass tubingconstricted to a tip at one end thereof and having a primer sealedtherein at the other end thereof. The length of glass tubing whichdefines the lamp envelope contains a combustible, such as shreddedzirconium foil, and a combustion supporting gas, such as oxygen. Theprimer comprises a metal tube and a charge of fulminating material on awire anvil coaxially supported therein. Operation of the lamp isinitiated by an impact onto the tube of the primer to cause deflagrationof the fulminating material on the wire anvil up through the tube toignite the combustible disposed in the lamp envelope.

Two significant and conflicting demands are made of the fulminatingmaterial for percussive flashlamps. The material must be very sensitiveso as to flash reliably upon impact. Deflagration of the fulminatingmaterial must be intense enough to reliably ignite the shredded metalliccombustible located at a distance from the fulminating material. On theother hand, highly sensitive fulminating materials tend to be violentburning, and when present in sufficient amounts to assure shredignition, the light output of the lamp and reliability of containmentbecome unacceptable. For example, a violet burning fulminating materialcan cause up to 50 percent reduction in lamplight output.

Basically, fulminating material employed in percussive-type photoflashlamps comprises a mixture of percussively reactive materials, a fuel andan oxidizer, arranged to ignite upon interparticle movement, such as ablend of red phosphorus and potassium chlorate. lntermixed with thepercussively reactive materials is a powdered combustible, incandesciblemetal, such as titanium. When the materials react, they ignite thepowdered metal and force incandescent particles thereof to spew into thebody of the envelope and ignite the shredded combustible metal.

During the course of development of the percussive flashlamp, it wasfound that different metallic constituents in the fulminating materialhad differing abilities to attenuate its explosive nature whilemaintaining high ignition reliability and sensitivity. Listed in orderof increasing attenuation ability are the metals zirconium, titanium,silicon, and boron. Extensive testing showed titanium to be the bestavailable choice with regard to overall explosive attenuation abilityand shred ignition reliability.

Ignition pastes for conventional filament type flash lamps usenitrocellulose as a binding resin, and organic solvents such as amylacetate as the vehicle. In an effort to increase the handling safety ofpercussive fulminating material, water was evaluated as the vehicle forapplying the fulminating material to the primer anvil, in conjunctionwith water soluble binding resins such as hydroxyethyl cellulose. Thefulminating material deposited from such an aqueous suspension was foundto be much more sensitive to impact than a similar material depositedfrom organic solvents. This enhanced sensitivity was attributed todeposition of the potassium chlorate onto the particles of redphosphorus, resulting in a more intimate mixture. Although these gainsin lamp sensitivity and reliability were significant, the new waterbased materials were found to retain a degree of hazard. It was found,for example, that a crust of dried material, generated enough heatduring flashing to ignite the adjacent aqueous suspension, and that thelatter would burn to completion. The burning violence of the wetmaterial varied inversely with the amount of water present.

Accidental drying or partial drying of the sensitive fulminatingmaterial constituted an ever present danger of fire or explosion in theproduction process. In order to restrict the danger involved in handlingand using the fulminating material it was prepared in small batches. Theamount allowed in any one container was Iimitated to a fraction of anounce of solid ingredients. The high cost of preparing numerous smallbatches was completely overshadowed by the lost machine production timerequired for frequent replacement or refilling of the small fulminatingmaterial dip cups.

In an effort to avoid the use of such hazardous materials in production,a two layer technique for applying fulminating material was evaluated inwhich the potassium chlorate and red phosphorus were not mixed. In thistechnique. separate coatings of potassium chlorate and of the redphosphorusmetal mixture were applied one over the other. Each componentwas prepared as a milled aqueous slurry containing the choseningredients along with a quantity of binding resin. Extensive testingand effort, however, failed to attain the degree of lamp reliability andphotometric performance with this two layer system that had beenachieved with the aqueous completely mixed material. The shortcomings ofsuch two layer structures is that only single-surface contact existsbetween the red phosphorus and potassium chlorate layers, whereas incompletely mixed material intimate bulk contact is attained.

A significantly improved technique for applying the fulminating materialwas then developed which proved to be safer and more economical forlarge scale production, while at the same time providing an impactsensitivity such that the flashlamps had a high degree of ignitionreliability and photometric performance. Referred to as an absorbedoxidizer process," the technique involves the deposition of anoxidizer-free layer made up primarily from red phosphorus and titanium,drying that coating, then dipping the coated anvil into a concentratedsolution of dissolved sodium chlorate which permeates thephosphorus-containing layer. when dried, a sensitive deposit offulminating material results which is similar in behavior to thatdeposited initially from a complete mixture. The chlorate salt componentof fulminating material applied in this manner is referred to as anabsorbed oxidizer."

In a small percentage of the lamps employing absorbed oxidizerfulminating materials, however, the fulminating material failed toignite the shredded combustible, even though the composition of thedried fulminating material was quantitatively the same as that of thecompletely mixed materials that gave good shred ignition reliability.The difference in performance is apparently caused by the nonhomogeneousdistribution of the absorbed sodium chlorate throughout the thickness ofthe fulminating material layer.

In view of the foregoing, the principal object of this invention is toprovide a fulminating material for percussive flashlamps that givesimproved shred ignition reliability while maintaining high impactsensitivity, good lamplight output characteristics, and manufacturingsafety and economy. Another object is to provide a safer more reliablepercussivetype photoflash lamp. A further object of the invention is toprovide an improved method of preparing and applying fulminatingmaterial on the primer anvil wire of a percussivetype photoflash lampwhich is safe and economical for large scale production and at the sametime provides improved shred ignition reliability without decreasingimpact sensitivity or lamplight output.

I have discovered that the addition of a small quantity of powderedcarbon to the fulminating material of percussive flashlampssignificantly reduces the incidence of shred ignition failure. When thecarbon burns upon ignition of the charge of fulminating material, itproduces carbon dioxide, which facilitates propulsion, or transport, ofthe incandescent titanium particles from the primer tube into the lampenvelope where the filamentary combustible shreds are located. Ofparticular importance, carbon achieves this result without at the sametime incurring the detrimental explosiveness that results when the redphosphorus content is increased for the same rnrno: (HR l purpose. Theaddition of soluble organic materials or more binding resin, even thoughbeing gas generators, is detrimental to the impact sensitivity andignition reliability of the composition because of the resultinginsulating" layer surrounding the particles of red phosphorus.

The optimum percentage of carbon to be added varies with the dimensionsand mechanical construction of the percussive flashlamp in which thefulminating material is to be used. I prefer approximately 1 percentbased on the weight of dried solids exclusive of the oxidizer, althoughquantities from 0.1 percent to 10.0 percent may be preferable with otherlamp types.

While not limited to such use, the addition of powdered carbon forfacilitating propulsion of the incandescent powdered metal isparticularly advantageous when employed in conjunction with the absorbedoxidizer process for applying fulminating material. That is, theadvantages of safety and economy provided by the absorbed oxidizertechniques are retained and further enhanced by an improvement inignition reliability.

Accordingly, an example of a very satisfactory method of preparing andapplying fulminating material in accordance with the invention is givenbelow.

First, an aqueous slurry is prepared having the following driedcomposition: titanium, 69.31 percent, red phosphorus 27.21 percent,hydroxyethyl cellulose, 1.19 percent, magnesium oxide, 061 percent;magnesium montmorillonite, 0.60 percent; carbon, 1.02 percent; sulphur,0.06 percent; and trichlorophenol, 0.01 percent. Water content isadjusted to give the desired coating thickness. The anvil is dipped intothis aqueous slurry and the resulting coating is dried.

The coated anvil wire is then dipped into an aqueous solution containingabout 25 percent by weight of dissolved sodium chlorate. Upon drying avery sensitive fulminating material coating results.

Alternative materials that can be used in place of powdered carboninclude combustible materials that are insoluble in the liquid vehicleused to apply the fulminating material to the primer and which givegaseous products of combustion. Further, the material must be stable forextended periods of time in intimate contact with sodium chlorate. Inparticular, the substance for facilitating propulsion of the powderedmetal may comprise any nonacidic carbon-containing compound which issubstantially insoluble in liquid vehicles commonly used in applyingfulminating material to the primer, such as water or amyl acetate.Finely powdered polymers such as, for example, cellulose or cellulosenitrate could be used.

Other chlorate salts which have cations not catalytically reactivetoward red phosphorus and which are soluble to the extent of l percentor greater by weight in water may be used as the oxidizers; for example,calcium chlorate, lithium chlorate, magnesium chlorate, and zincchlorate, however, the extreme deliquescence of these materials mayrender their use in flashlamps more difficult with regard to drying andmaintaining the coating dry prior to hermetic closure of the flashlamp.Similarly phosphorus sesquisuli'ide may be used in place or redphosphorus, if desired, although a slight loss in sensitivity may benoted. Further, although titanium is preferred, other powderedcombustible, incandescible metals may be employed, such as zirconium orboron.

In the accompanying drawing, the single FIGURE is an elevational viewpartly in section of a percussive-type photoflash lamp with which acharge of fulminating material prepared in accordance with thisinvention may be employed. The lamp comprises a length of glass tubingdefining an hermetically sealed lamp envelope 2 constructed at one endto define an exhaust tip 4 and shaped to define a seal 6 about a primer8 at the other end thereof. The primer 8 comprises a metal tube 10 awire anvil 12 coated with a charge of fulminating material 34. Acombustible such as filamentary zirconium 16 in a combustion supportinggas such as oxygen are disposed within the lamp envelope. The wire anvil12 is centered within the tube 10 and held in place by a crimp 18 justabove the head 20 of the anvil. Additional means, such as lobes 22 onwire anvil 12, are also used to aid in stabilizing and supporting itsubstantially coaxial within the primer tube 10 and insuring clearancebetween the fulminating material 14 and the inside wall of the tube 10.A refractory bead 24, fused to the wire anvil 12 just above the innermouth of the primer tube 10, eliminated burn-through and functions as adeflector to deflect and control the ejection of hot particles offulminating material from the primer.

In conclusion, the present invention incorporates an additional gasgenerating fuel in the fulminating material for percussive flashlamps inorder to provide efficient transport to the incandescent particles fromthe primer to the envelope to thereby promote high shred ignitionreliability without decreasing impact sensitivity or lamp light output.Such a propellant is particularly advantageous in the primer structureillustrated in the drawing. Of additional significance, the inventiveprinciples described significantly enhance the commercial manufacture ofpercussive flashlamps by the much safer absorbed oxidizer process.

What I claim is:

1. A photoflash lamp comprising:

an hermetically sealed, light-transmitting envelope;

a quantity of filamentary combustible material located within saidenvelope;

a combustion-supporting gas in said envelope;

and a primer secured to one end of said envelope and in communicationtherewith, said primer including a charge of percussively ignitablefulminating material comprising a phosphorus fuel, a chlorate saltoxidizer, a powdered combustible, incandescible metal, and a substancefor facilitating the propulsion of said powdered metal from said primerinto said envelope when said charge is ignited, said last-mentionedsubstance consisting of powdered carbon or a powdered, nonacidiccarbon-containing compound which is substantially insoluble in liquidvehicles commonly used in applying said fulminating material to saidprimer.

2. The combination of claim 1 in which said chlorate salt is an absorbedoxidizer having a water solubility greater than 15 percent by weight anda cation not catalytically reactive toward phosphorus.

3. The combination of claim 1 in which said last-mentioned substanceconsists of powdered carbon or a powdered, nonacidic organic carboncompound which is substantially insoluble in liquid vehicles commonlyused in applying said fulminating material to said primer.

4. The combination of claim 3 in which said powdered carbon or carboncompound comprises not less than 0.1 percent and not more than 10percent of the dry weight of said fulminating material exclusive of saidoxidizer.

5. The combination of claim 3 in which said fuel is red phosphorus, saidoxidizer is sodium chlorate, and said powdered metal is titanium.

6. The combination of claim 1 in which said primer includes a tubesealed in said end of said envelope and having an exposed segmentoutside said envelope, and a wire anvil located substantially coaxialwithin said tube, said fulminating material being a coating on said wireanvil located intermediate its ends and on that segment of said wireanvil located in said exposed segment of said tube but spaced from theinside wall thereof.

7. The combination of claim 6 in which said fuel is red phosphorus, saidoxidizer is absorbed sodium chlorate, said powdered metal is titanium,and said propulsion facilitating substance is powdered carbon or apowdered, nonacidic organic compound which is substantially insoluble inliquid vehicles commonly used in applying said fulrninating material tosaid wire anvil.

8. The combination of claim 6 in which the dried composition of saidfulminating material exclusive of said oxidizer comprises about 69.31percent titanium, about 27.21 percent red phosphorus, about l.l9 percenthydroxyethyl cellulose, about 0.61 percent magnesium oxide, about 0.60percent magnesium montmorillonite, about 1.02 percent carbon, about 0.06percent sulfur, and about 0.01 percent trichlorophenol.

9. The method of preparing fulminating material and applying saidfulminating material on a primer anvil wire of a percussive-typephotoflash lamp, said method comprising:

Preparing a slurry comprising a liquid vehicle, red

phosphorus, a powdered combustible, incandescible metal, and powderedcarbon or a powdered, nonacidic carbon-containing compound which issubstantially insoluble in said liquid vehicle;

coating said wire with said slurry;

drying said coated wire;

and permeating said coating on said wire with a chlorate salt solutioncontaining at least percent by weight of dissolved chlorate salt.

10. The method of claim 9 in which the step of coating said wire isperformed by dipping said wire into said slurry, and the last step isperformed by dipping said coated wire into said chlorate salt solution.

11. The method of claim 9 in which said slurry is prepared by usingwater as the liquid vehicle, said powdered metal is titanium, and saidpowdered carbon or carbon compound comprises not less than 0.1 percentand not more than 10 percent of the weight of the materials in saidslurry when dried.

12. The method of claim 10 in which said slurry is prepared by usingwater as the liquid vehicle and has a dried composition comprising about69.31 percent titanium, about 27.21 percent red phosphorus, about l.l9percent hydroxyethyl cellulose, about 0.61 percent magnesium oxide,about 0.60 percent magnesium montomorillonite, about 1.02 percentcarbon, about 0.06 percent sulfur, and about 0.01 percenttrichlorophenol, and in which said chlorate salt solution is prepared bydissolving sodium chlorate in water to provide an aqueous solutioncontaining about 25 percent by weight of said chlorate.

2. The combination of claim 1 in which said chlorate salt is an absorbedoxidizer having a water solubility greater than 15 percent by weight anda cation not catalytically reactive toward phosphorus.
 3. Thecombination of claim 1 in which said last-mentioned substance consistsof powdered carbon or a powdered, nonacidic organic carbon compoundwhich is substantially insoluble in liquid vehicles commonly used inapplying said fulminating material to said primer.
 4. The combination ofclaim 3 in which said powdered carbon or carbon compound comprises notless than 0.1 percent and not more than 10 percent of the dry weight ofsaid fulminating material exclusive of said oxidizer.
 5. The combinationof claim 3 in which said fuel is red phosphorus, said oxidizer is sodiumchlorate, and said powdered metal is titanium.
 6. The combination ofclaim 1 in which said primer includes a tube sealed in said end of saidenvelope and having an exposed segment outside said envelope, and a wireanvil located substantially coaxial within said tube, said fulminatingmaterial being a coating on said wire anvil located intermediate itsends and on that segment of said wire anvil located in said exposedsegment of said tube but spaced from the inside wall thereof.
 7. Thecombination of claim 6 in which said fuel is red phosphorus, saidoxidizer is absorbed sodium chlorate, said powdered metal is titanium,and said propulsion facilitating substance is powdered carbon or apowdered, nonacidic organic compound which is substantially insoluble inliquid vehicles commonly used in applying said fulminating material tosaid wire anvil.
 8. The combination of claim 6 in which the driedcomposition of said fulminating material exclusive of said oxidizercomprises about 69.31 percent titanium, about 27.21 percent redphosphorus, about 1.19 percent hydroxyethyl cellulose, about 0.61percent magnesium oxide, about 0.60 percent magnesium montmorillonite,about 1.02 percent carbon, about 0.06 percent sulfur, and about 0.01percent trichlorophenol.
 9. The method of preparing fulminating materialand applying said fulminating material on a primer anvil wire of apercussive-type photoflash lamp, said method comprising: Preparing aslurry comprising a liquid vehicle, red phosphorus, a powderedcombustible, incandescible metal, and powdered carbon or a powdered,nonacidic carbon-containing compound which is substantially insoluble insaid liquid vehicle; coating said wire with said slurry; drying saidcoated wire; and permeating said coating on said wire with a chloratesalt solution containing at least 15 percent by weight of dissolvedchlorate salt.
 10. The method of claim 9 in which the step of coatingsaid wire is performed by dipping said wire into said slurry, and thelast step is performed by dipping said coated wire into said chloratesalt solution.
 11. The method of claim 9 in which said slurry isprepared by using water as the liquid vehicle, said powdered metal istitanium, and said powdered carbon or carbon compound comprises not lessthan 0.1 percent and not more than 10 percent of the weight of thematerials in said slurry when dried.
 12. The method of claim 10 in whichsaid slurry is prepared by using water as the liquid vehicle and has adried composition comprising about 69.31 percent titanium, about 27.21percent red phosphorus, about 1.19 percent hydroxyethyl cellulose, about0.61 percent magnesium oxide, about 0.60 percent magnesiummontomorillonite, about 1.02 percent carbon, about 0.06 percent sulfur,and about 0.01 percent trichlorophenol, and in which said chlorate saltsolution is prepared by dissolving sodium chlorate in water to providean aqueous solution containing about 25 peRcent by weight of saidchlorate.